Gerber files are the ones produced for manufacuring of the boards. Their measurements are EXACTLY as the produced board.
They are however quite large are difficult to modify since they're made of lines and dots.

MGC design files. These are the actual designs we have used. they are in a 'released & editable' format which means that they include EVERYTHING necessary for the design.
They can be converted by some other major CAD-systems (CADENCE et.al.), but probably not by any existing mechanics CAD-system.